Defluoridation of drinking water by magnesium and aluminum electrocoagulation in continuous flow-rate: a response surface design.

The goal of this research is to apply an electrocoagulation process in continuous flow for the defluoridation of drinking water. Two sampling sites were studied, Temascalcingo (T), Mexico state and Jerecuaro (J), Guanajuato, with fluoride (F-) concentrations above the norms (2.3 mg L-1 and 4.5 mg L-1, respectively). In addition, a second Temascalcingo sample was enriched (TE) to 9.2 mg L-1 F- to study the effect of the F- concentration. A response surface design was proposed through a Box-Behnken model, and the variables studied were electrode system, flow-rate and current intensity. 51 experiments were performed with T-site to determine the best operating conditions for the system. These conditions were applied to the J-site. The experiments for T, Al/Al system achieves an F- concentration within permissible limits (0.72 mg L-1 F-) at 10 min of treatment, 0.2 A (Current density j 48.78 A m-2) and 10 mL min-1 with a removal efficiency of 68.69%, and after 160 min, the removal increased to 99.56%. AlMg/AlMg needs 10 min to achieve a concentration of 0.75 mg L-1 F- at 0.2 A (j 25 A m-2), 16 mL min-1 with a removal efficiency of 67.39%, and after 100 min, the removal is increased to 92.17%. An important and novel advantage is the use of AlMg allows an acceptable removal of F- (<1.5 mg L-1) at high and low concentrations in short periods of time; this also allows save energy costs and the effluent is free of residual aluminum, avoiding side effects.